problem might be the potential for fans to cancel the direct debit if they were doing badly
I'm sure if it could be set up in a fixed contract.
Personally, I think it would be an appealing prospect for the 15-18 game a season regulars (like myself) to get to more/all the games.
I don't think the club would lose money, as floating fans would be come to (and therefore paying money for) games that they previously/otherwise would have come to. For example with my direct debit suggestion of £250 in total (£25per month for 10months), equates to just over 19 games at the regular gate price of £13. By contractually obliging fans to pay by direct debit, the club would guaranteed a steady flow of income into the club. Also the possibility of increased attendances hopefully lead to and increase in spending on programs and pies etc. as regulars started attending not most, but every fixture.
Another way of looking at is this:
'Fan A' turns up to every game and pays £13 on the gate (£299 over the season). Can the club risk the fact that such a fan will come to every game and not miss a few therefore essentially paying £250 anyway?
'Fan B' turns up to 18 games every season and pays £13 on the gate (£234 over the season). Is it worth the risk that they only come to/pay for 16 matches? Or would the chance of a season ticket paid in monthly installment costing an extra £16 over the year be appealing to him/her?